BaseTools ConvertMasmToNasm: Fix running script outside of a git tree

BaseTools ConvertMasmToNasm: Fix running script outside of a git tree

The script previously would hit an exception if it was run outside of
a git tree.

The exception looked like:

edk2/BaseTools/Scripts/ConvertMasmToNasm.py Version 0.01
Traceback (most recent call last):
  File "edk2/BaseTools/Scripts/ConvertMasmToNasm.py", line 986, in <module>
    ConvertAsmApp()
  File "edk2/BaseTools/Scripts/ConvertMasmToNasm.py", line 984, in __init__
    ConvertAsmFile(src, dst, self)
  File "edk2/BaseTools/Scripts/ConvertMasmToNasm.py", line 209, in __init__
    CommonUtils.__init__(self, clone)
  File "edk2/BaseTools/Scripts/ConvertMasmToNasm.py", line 69, in __init__
    self.gitemail = clone.gitemail
AttributeError: ConvertAsmApp instance has no attribute 'gitemail'

Fixes: https://github.com/tianocore/edk2/issues/63
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>